Problems of bone tissue restoration include avoiding free space between bone fragments, avoiding filling the space previously occupied by lost bone with connective tissue, and controlled evacuation of the space to leave room for the newly growing tissue.
Solution of the problem lies in the development of biocompatible polymers biodegradable under the action of body fluids within preset periods of time and technological processes for making diversely shaped finished products from such polymers, as well as technology for imparting therapeutic properties to such polymer products.
Known structures made of biologically inert materials are aimed at permanent replacement of a missing portion of bone and thus render it completely impossible to form fresh bone tissue of the patient's own making at the place involved.
A prior-art device for external immobilization of bone fragments (cf. I. A. Moshkovich, Operative Orthopedics, 1983, Meditsina Publishers, Moscow, pp. 224-225 (in Russian)) has a number of rings inter connected through rods and provided with intramedullary pins. Application of this device enables one to elongate a human limb by daily repeated gradual extension of the bone fragments by gradually increasing the distance between the rings. An extension cycle lasts from 20 to 80 days.
Such a device, however, is suitable for stretching sound limbs only. Besides, its application involves much work by medical staff for a prolonged period of time. Also, there is a source of permanent danger of infection at the place of introduction of the transverse pins, which may also cause contraction of ligaments. The device cannot be used where there are extensive total bone defects due to a complicated injury or gunshot wounds.
A state-of-the-art device for restoration of a missing portion of a tubular bone (cf. Biomekhanika, 1975, Riga, V. K. Kalnberz, et al. Clinico-biomechanical requirements imposed on the endoprosthesis of the femoral diaphysis, pp. 365-366 (in Russian)) is known to comprise a central metallic rod and a tubular element based on biologically inert composite materials, such as polymers or inorganic substances, the tubular element being fitted on the rod. The configuration and dimensions of the tubular element correspond to the missing portion of bone. During surgery, the rod is introduced into the medullary canals of the tubular bone fragments, then the tubular element is installed on the rod at the place of the missing portion of bone and fixed to the bone fragments. However, such a tubular element is very difficult to make according to the individual dimensions of patient's injury. It is extremely difficult to combine an artificial bone with the bone matrix; the bone tissue is liable to resorb at the place of contact with the artificial bone and the reaction to a large foreign body manifests itself continuously after implantation of the artificial bone. The possibility of replacement by genuine bone of the patient is ruled out completely.